So, didn't really pay attention to the article, but wow, that spinning mask[0] in interesting!
Somehow, the effect doesn't work looking at only the forehead[1] which I would have assumed means because my brain doesn't recognize it as a "face". However, the effect does work for me still only looking at the neck[2] which I can't explain other than something with the shading?
the surface normals don't change when the mask rotates from the front to the back so the lighting appears to "change direction". I think looking at the edges gives you more cues to see that the mask is rotating vs only having the reversing lighting cues in the center
